The present invention relates to a portable telephone, a diffuser and a lighting device both of which are provided in the portable telephone, in particular to the portable telephone having a back light, and the like which uniformly emit a light on input buttons, the diffuser and the lighting device both of which are provided in the portable telephone.
In a conventional portable telephone, a light emitting element, such as a light emitting diode (hereunder called LED), and the like is provided, for example, near input buttons, such as numeral keys, or the like. The light emitting element is adjusted to emit a light every time that any one of the input buttons are pushed on by an user. Accordingly, the conventional portable telephone can be used by the user even in the darkness.
The conventional portable telephone comprises a housing, a plurality of input buttons, a substrate, and a plurality of LEDs each of which is mounted on the substrate and located under a part of the housing between the input buttons. The input buttons are consisting mainly of resins, respectively. Each of the resins includes a diffuser including a diffusing material on which a light from the LED is incident and through which the light is emitted towards an upper side of the input buttons. A surface of the resin defines a lighting surface which transmits or reflects the light from the LED. The conventional portable telephone can be used even in the darkness by driving the LED, when any one of the input buttons are pushed on by an user.
However, a strength of a light projected from the resin actually becomes smaller as the light becomes remote from the LED. This is not only because the transmission light is fewer than the transmission light at the lighting plane but also because the progressing light is not adjusted to transmit the lighting plane. The strength of the light projected from the resin becomes smaller as the light becomes remote from the LED. As a result, literatures depicted in the input buttons sometimes cannot be seen sufficiently, when the conventional portable telephone is in the darkness. Some proposals are made for solving this problem. For example, numbers of the LEDs are increased. Further, a strength of emitting light in the LED is increased. Moreover, a distance between the LED and the lighting plane is designed to be longer.
However, in a case that the numbers of the LEDs are increased or that the strength of emitting light in the LED is increased, power consumption of the conventional portable telephone is also increased. Further, in a case that the distance between the LED and the lighting plane is designed to be longer, thickness of the conventional portable telephone sometimes becomes larger.